The present invention relates to medical diagnostic X-ray imaging, and more specifically relates to adjustment of pictures corresponding to x-ray images.
Today, doctors and technicians commonly have access to very sophisticated medical diagnostic X-ray imaging devices. Typically during the operation of an X-ray imaging device, an X-ray source emits X-ray photons under very controlled circumstances. The X-ray photons travel through a region of interest (ROI) of a patient under examination and impinge upon a detector. In the past, X-ray imaging devices employed rudimentary film based detectors. However, recent developments have led to solid-state detectors comprised of a grid of discrete detector elements that individually respond to exposure by X-ray photons. Regardless of the detector used, however, the goal remains the same, namely to produce a clear resultant image of preselected structures of interest (e.g., specific types of tissues) within the ROI.
There is an inherent difficulty associated with producing a clear resultant image, however. In particular, because the X-ray photons travel through the entire patient, the image formed on the detector is a superposition of all the anatomic structures through which X-ray photons pass, including the preselected structures of interest. The superposition of anatomic structures is sometimes referred to as xe2x80x9canatomic noisexe2x80x9d. The effect of anatomic noise on the resultant image is to produce clutter, shadowing, and other obscuring effects that render the resultant image much less intelligible than the ideal clear resultant image.
Attempts to reduce the effects of anatomic noise include, for example, xe2x80x9cdual-energyxe2x80x9d imaging. When employing dual-energy imaging, a doctor or technician acquires an image at high average X-ray photon energy, and an image at low average X-ray photon energy. Because different internal structures absorb different X-ray photon energies to different extents, it has been possible to combine the two resultant images to suppress anatomic noise according to:
SB(x,y)=exp[log (H(x,y))xe2x88x92w log (L(x,y))], (0 less than w less than 1),
where SB is the decomposed image achieved through the log subtraction at a specific cancellation parameter w, H(x,y) is an image obtained at high energy, and L(x,y) is an image obtained at low energy. By varying w, SB becomes a decomposed image of either soft tissue (i.e. soft structure) or of bone (i.e. hard structure).
Radiologists often desire to review both a standard image, which is often the original high-energy image, and the decomposed image of soft structure at the same time or in sequence. Unfortunately, the decomposed image of soft structure has a different contrast than the standard image. When the standard image and the decomposed image of soft structure are reviewed on a computer monitor, such that the user toggles back and forth between the two images, the difference in contrast may make it difficult to compare the images and to identify subtle features and differences between the images. Viewing the images in this format necessitates that the radiologist learn to read the decomposed image of soft structure differently.
The same problem is experienced when viewing the two images in other forms, such as printed on paper or film, for example. Each device (i.e. computer monitor, printer, and the like) has multiple transfer functions available, which relate pixel values to the final displayed intensity of the image. It may be possible to apply a different image transfer function to either the standard image or the decomposed image before reviewing the images in an effort to more closely match the contrast levels. However, this process is time consuming and may require the user to apply a number of different image transfer functions in a trial and error process to achieve an acceptable contrast for both images. Additionally, printing devices may require some manual manipulation to adjust the contrast of the two images, resulting in additional processing time and cost. Thus, a need has long existed in the industry for a method for adjusting the contrast of decomposed images compared to the contrast of a standard image that addresses the problems noted above and previously experienced.
One method embodiment of the invention is useful in an X-ray system arranged to display a first picture of an object generated in response to an X-ray first range of energy levels and an X-ray second range of energy levels different from the first range of energy levels and arranged to display a second picture of the object generated in response to substantially a single range of X-ray energy levels. In such an environment, a contrast level of the first picture is adjusted relative to a contrast level of the second picture by transmitting X-rays at the first range of energy levels and second range of energy levels to generate a first image representing the object in response to the first range of energy levels and to generate a second image representing the object in response to the second range of energy levels. A first decomposed image is obtained from the first and second images according to a first decomposition algorithm, and a second decomposed image is obtained from the first and second images according to a second decomposition algorithm. A contrast-adjusted image is calculated in response to the first and second decomposed images. The first picture is displayed in response to the contrast-adjusted image, and the second picture also is displayed.
One apparatus embodiment of the invention also is useful in an X-ray system arranged to display a first picture of an object generated in response to an X-ray first range of energy levels and an X-ray second range of energy levels different from the first range of energy levels and arranged to display a second picture of the object generated in response to substantially a single range of X-ray energy level. In such an environment, a contrast level of the first picture is adjusted relative to a contrast level of the second picture by providing a source of the X-rays at the first and second ranges of energy levels. An image sensor is arranged to generate a first image representing the object in response to X-rays at the first range of energy levels and to generate a second image representing the object in response to X-rays at the second range of energy levels. A processor is arranged to calculate a first decomposed image from the first and second images according to a first decomposition algorithm, calculate a second decomposed image from the first and second images according to a second decomposition algorithm and calculate a contrast adjusted image in response to the first and second decomposed images. A display is arranged to display the first picture in response to the contrast-adjusted image and to display the second picture.
By using the foregoing techniques, X-ray pictures may be contrast adjusted with a degree of accuracy and ease previously unattainable. Such adjustment makes the pictures easier to use and decreases the amount of training required before the pictures can be accurately interpreted.